The most common melting temperature range for standard solders (like SnPb or SnPbAg) is in the 180°C to 190°C range, and the most popular Pb-free alloys melt in the 220°C to
225°C. But, what do you do if you need a solder that reflows at a lower temperature? You might be soldering temperature-sensitive components. Or you might be performing a step-soldering operation, using a standard alloy for the initial operation, and requiring a lower temperature solder for a subsequent step.
In addition to offering many desirable physical properties (malleability, ductility, fatigue resistance. etc.), indium alloys offer relatively low melting points.

Another low temperature need is not related to soldering. It simply requires that the material melt at a precise temperature. Indium is a constituent of many fusible alloys (used in fuse applications where the metal melts at a specified temperature, triggering a desired action - like a fire sprinkler to release water).